Summary of pipette basics

Pipettes achieve different accuracy and precision through a variety of designs, including simple pipettes made of a piece of glass, to complex adjustable or electronically controlled pipettes. The accuracy of measurement varies greatly depending on the type . Today, Sister Xiaoxi will have a good chat with everyone about pipettes.

Pipettes, also known as "quantitative pipettes", "pipettes", and "pipettes" are experimental instruments designed to measure the volume of liquids and transfer them to other containers. Often used in biological experiments or chemical experiments.

Classification and principle of pipettes

Common pipettes can be divided into the following five types, namely, exhaust micropipette, positive displacement pipette, positive displacement pipette, graduated pipette, and Pasteur pipette.

1. Exhaust type micro pipette

Exhaust type micropipette, often called "exhaust type pipette" or "pipette gun" for short, is an adjustable pipette used to measure the volume of 0.1-1000 microliters. This type of pipette requires a disposable tip, which is in contact with the liquid. The exhaust type micropipette is driven by a piston to discharge air, whereby the vertically moving metal or ceramic piston creates a vacuum in the closed tube. When the piston pumps upwards, the second half of the gas is compressed, and the first half of the space becomes a vacuum. At this time, the liquid near the tip of the gun enters the vacuum part, and then can be transferred or discharged again. This pipette has high accuracy and precision and is suitable for routine pipetting operations. However, because it relies on the movement and compression of gas, the accuracy is greatly affected by environmental conditions, especially temperature, air pressure, and user technology. Therefore, this instrument must be properly stored and calibrated, and the user must also be trained to practice correct and stable operation techniques.

Common brands of exhaust micropipettes include Eppendorf, Gilson, ErgoOne, etc.

, Positive displacement pipette

This kind of pipette is similar to the vented pipette, but it is less used, usually used to avoid pollution, or used for small, volatile or viscous substances, such as volatile organic compounds, DNA, etc. The main difference is that the disposable tip is a Microsyringe with a piston, the piston is made of plastic, and the piston is in direct contact with the liquid to suck and discharge the liquid.

3. Volumetric pipette

Volumetric pipettes are also called "pipettes", with extremely high precision (four significant digits). This type of pipette has a ball, and there is a graduation line above the ball, which only identifies the pipette The fixed volume. Typical models have volumes of 10, 25, and 50 milliliters. Volumetric pipettes are often used to prepare solutions from basic materials, or to prepare titrants.
4. Scaled pipette

Graduated pipettes, also known as graduated pipettes, graduated pipettes, etc., are long glass tubes with a series of graduated lines, which can suck different volumes of liquid. Such graduated pipettes usually have 5, 10, 25, and 50 ml specifications. The graduated pipette has a positive and negative error range, which is 0.6% to 0.4% of the theoretical volume when measured at 20°C. Graduated pipettes are manufactured according to ISO standards for accuracy and graduation arrangements. Type A has higher accuracy than type B.
Precautions:

1. The pipette (pipette) should not be dried in the oven.

2. The pipette (pipette) can't pipette solutions that are too hot or too cold.

3. The same pipette should be used as much as possible in the same experiment.

4. After the pipette is used, it should be rinsed with tap water and distilled water immediately and placed on the pipette rack.

5. Pipettes and volumetric flasks are often used together, so the relative volume of the two is often calibrated before use.

6. When using the pipette, in order to reduce the measurement error, the starting point should be the top scale (0 scale) every time, and the required volume of solution should be discharged down instead of sucking as much volume as needed.

7. There are old style and new style pipettes. The old style pipe body is marked with the word "Blow". You need to use an ear wash ball to blow out the residual liquid at the mouth of the pipe. There is no new type, do not blow out the residue of the nozzle, otherwise it will cause too much liquid to be taken.
5. Pasteur straw

The Pasteur pipette is a plastic or glass pipette used to transfer a small amount of liquid, but it is not marked with any volume scale or guideline. Pasteur pipettes are more commonly called droppers and chemical droppers.


The structure of the pipette

At present, the commonly used venting micropipette and positive displacement pipette in laboratories are: components for sucking and discharging liquid, volume adjustment dial, disposable pipette tip, pipette ejector button, and pipette ejector rod.

The difference between vented and positive displacement pipettes

The accuracy of the exhaust micropipette is greatly affected by environmental conditions, and the correct pipetting operation can minimize the impact of the environment.

The correct suction operation of commonly used exhaust micropipettes:

A. Hold the flat part of the micropipette in the palm in a vertical direction, and press the operation button to the first stop position

B. Immerse the tip just below the liquid level, release the button steadily, and then wait a while until the liquid enters the tip, make sure there are no bubbles in the tip

C. Gently press the operating button to the first stop point, and after about 1 second, continue to press the operating button down to the second stop point of this operation. The function of this operation is to drain the solution in the mouth

D. Release the button to return to the starting position

as the picture shows


The positive displacement pipette sucks the volume of the actual scale and a certain amount of excess liquid, and its operation method is slightly different from that of the exhaust type:

A. Hold the flat part of the micropipette in the palm in a vertical direction, and place the button in the second stop position

B. Just submerge the tip below the liquid surface. Release the button steadily, the liquid enters the tip, and make sure that there are no bubbles in the tip

C. Put the button at the first stop position to discharge the liquid, and keep the operation button at the first stop position, so that a small amount of liquid that does not include the pipetting volume range remains in the nozzle

D. Press the button in the second stop position to discard excess liquid

as the picture shows


Use specifications and precautions

1. Use the right tip

In order to ensure better accuracy and precision, it is recommended that the pipetting volume be within the range of 35%-100% of the tip.

2. Set the pipetting volume

Adjusting from a large range to a small range is the normal adjustment method, just rotate the scale counterclockwise

When adjusting from a small range to a large range, it should first be adjusted to exceed the set volume scale, and then back to the set volume, so as to ensure the accuracy of the pipette

3. Installation of the suction head

For most brands of pipettes, especially multi-channel pipettes, it is not easy to install the tip: in order to pursue a good seal, insert the pipette vertically into the tip, rotate it half a turn left and right, and tighten it. There are also people who use the pipette to repeatedly hit the tip to tighten, but this operation will cause the tip to deform and affect the accuracy, and severely damage the pipette, so such operations should be avoided. Some multi-channel pipettes are equipped with O-rings, matched with a tip with a front stop point, and an ideal seal can be achieved with a light pressure.

4. The immersion angle and depth of the tip

The immersion angle of the tip is controlled within 20 degrees of inclination, and it is better to keep it upright; the tip immersion depth is recommended as follows:


5. Suction head rinse

For samples at room temperature, tip rinsing can help improve accuracy; but for samples with high or low temperature, tip rinsing will reduce the accuracy of the operation. Please pay special attention to users.

6. Liquid suction speed

The pipetting operation should maintain a smooth and appropriate suction speed; too fast aspiration speed will easily cause the sample to enter the sleeve handle, causing damage to the piston and seal ring and cross-contamination of the sample.

7. Placement of the pipette

The pipette that sucks liquid should not be placed flat. The liquid in the tip can easily contaminate the inside of the gun and may cause the gun's spring to rust. The scale of the pipette should be adjusted to the maximum after each experiment, so that the spring returns to the prototype to extend the service life of the pipette.

8. The tip needs to be sucked in advance

In order to obtain higher accuracy, the tip needs to take a sample solution in advance, and then formally pipette, because when sucking serum protein solution or organic solvent, a layer of "liquid film" will remain on the inner wall of the tip, resulting in a small discharge volume And produce errors.

9. Compensation

Liquids with high concentration and viscosity will cause errors. In order to eliminate the error, the compensation amount can be determined by experiment. The compensation amount can be set by changing the reading of the reading window with the adjustment knob.

10. The pipette is strictly forbidden to absorb highly volatile and corrosive liquids.

11. Pipetting volume

Do not use a large-range pipette to pipette small volumes of liquid, so as not to affect accuracy. At the same time, if you need to pipette a larger amount of liquid outside the measuring range, please use a pipette to operate

Tips for using pipettes

1. It is not advisable to bounce back quickly when sucking liquids. It is necessary to do this even more when sucking high-viscosity liquids. Check whether there are foreign objects in the nozzle before sucking liquids.

2. Maintain the correct posture when pipetting; do not hold the pipette tightly all the time, use a pipette with a finger hook to help relieve hand fatigue; change hands frequently if possible.

3. Regularly check the sealing condition of the pipette. Once the seal is aging or leakage occurs, the sealing ring must be replaced in time.

4. Check the pipette 1-2 times a year (depending on the frequency of use).

5. For most pipettes, a layer of lubricating oil should be applied to the piston before use and after a period of use to maintain tightness;

6. Daily maintenance and repair of pipettes

At the end of use, adjust the range of the pipette gun to the maximum scale, so that the spring is in a relaxed state to protect the spring;

When there is liquid in the pipette nozzle, it is strictly forbidden to place the pipette horizontally or upside down to prevent the liquid from flowing into the piston chamber and corroding the pipette piston;

Use the correct method to install the suction head, remember not to use too much force, let alone the method of chopping the suction head for installation;

Clean the pipette regularly. You can use soapy water, 60% isopropanol, 70% ethanol and other non-corrosive detergents, then wipe it with distilled water and let it dry naturally. Before autoclaving, make sure that the pipette can adapt to high temperatures.

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